1. Field of the Invention
The present invention relates to the measurement and cutting of work pieces, and, more specifically but not exclusively, to apparatuses that may be used to guide movement of a cutting instrument, such as a circular saw, across a work piece at a desired measurement from an edge of the work piece.
2. Description of the Related Art
Circular saws can be difficult and dangerous to use for a number of reasons. For example, circular saws typically include a cutting guide that requires the user to stand very close to the circular saw and to lean over the saw in order to view the cutting guide. This is because the cutting guide is conventionally located on the opposite side of the circular saw, away from the user. This further requires the user to place his or her abdomen, waist, leg and/or thigh closer to the circular saw blade, while simultaneously concentrating on keeping the cutting guide on a line that was previously drawn on the work piece, to result in a somewhat even, but not necessarily accurate, cut. As one of Popular Mechanics magazine's top five most dangerous tools, the circular saw's blade travels at 120 miles per hour and is a major cause of injury, especially to “do-it-yourselfers.” Although professional carpenters might be more prepared to handle the hazards of using a circular saw due to their experience with the tool, even carpenters suffer from daily fatigue that increases as the long workday progresses, as well as exposure to the elements of a typical outdoor or construction-site work environment. These factors contribute to the likelihood of accidental injury from circular saw use, even among experienced users.
Circular-saw kick-up and kickback can be a dangerous problem. Kick-up occurs when the circular blade of a power saw binds or grabs a work piece being cut, which throws the spinning saw and its cutting blade up toward the user. Similarly, kickback occurs when the circular blade of a power saw binds or grabs a work piece being cut, which throws the spinning saw and its cutting blade back toward the user. Typically, the kick-up and kick-back motion occur together such that the saw is forced away from the surface of the work piece and backward toward the user. The motion of kick-ups and kickbacks can occur so quickly as to make it difficult or impossible for the user to avoid injury. Although various guides for circular saws are known, none of these guides provide protection for the user from kick-ups and kickbacks.
U.S. Pat. No. 7,020,978 to Nelson discloses an adjustable tool guide that provides no protection from circular-saw kickback. This tool guide is used in conjunction with a clamp that holds the tool guide in position over the work piece, so that the user can place both hands on the circular saw. Disadvantageously, this procedure adds an extra step that slows the cutting process, and further, the '978 patent does not specifically address the potential for harm to the user due to kick-up, kickback, or other safety concerns. In practicality, professional users seldom clamp down their smaller work piece and instead usually hold the work piece with one hand while holding the circular saw with the other. This scenario provides little protection from circular saw kick-up and kickback and increases the user's exposure to the moving blade. Further, although the tool guide of the '978 patent has an integrated tape measure with means for adjusting the effective extension length of the tape with respect to the guide, this arrangement can be unreliable because the tape adjustment assembly is pulled against the work piece each time the device is used. This pulling of the tape adjustment assembly promotes and repeatedly increases the potential for inaccuracy due to loss of calibration. To ensure accuracy in the cutting process and subsequent results, the tool guide of the '978 patent must constantly be recalibrated, e.g., by manually verifying the tape adjustment assembly using a second tape measure. Also, since most users do not own multiple circular saws, adjustability of the tool guide can be more of a detriment than a benefit, due to this constant recalibration necessitated by a number of moving parts.
U.S. Pat. No. 6,393,710 to Hastings discloses a combination tape measure and straight-edge apparatus that provides no kick-up or kickback protection from a circular saw. Unless the device is made to be extremely large, passing a circular saw adjacent to the device can be difficult. This is because the tape-measure mounting device is stationary and centrally positioned within the device, thereby providing insufficient clearance for a circular saw motor to pass by the mounted tape measure. The '710 patent provides no means for positioning the tape measure further away from the circular saw in a way that provides the necessary clearance.
U.S. Pat. No. 4,483,071 to Te Kolste also discloses a power-driven circular-saw guide that provides no kick-up or kickback protection. The device of the '071 patent includes a built-in, fully-extended measuring device or rule permanently mounted and extended to the length of the device. The size limitation of the device that is necessary to make the device portable and easy to carry limits the length of material that can be cut, making the cutting of commonly-available building material (for example, 2″×4″ framing lumber in 6- to 16-foot lengths) impractical. The device also includes a wing-nut clamp that needs constant attention to ensure cutting-length accuracy.
U.S. Patent Application Pub. No. 2007/0277389 also discloses an attachable circular-saw guide that provides no kick-up or kickback protection. The device of the '389 application is an attachment to a circular saw that increases the saw's handling weight. Moreover, the '389 application discloses a device for cutting a workpiece at various angles that limits the length of material being cut, making the cutting of commonly-available building material (for example, 2″×4″ framing lumber in 6- to 16-foot lengths) impractical.